Epithelia form dynamic barriers between tissue compartments and modulate their permeability properties during physiological and pathophysiological processes. Inappropriate maintenance or control of epithelial paracellular barriers contributes to many disease processes, especially inflammation. Cadherins are particularly important for the regulation of paracellular permeability in epithelia as well as endothelia, and the cadherin-catenin system has been directly implicated in inflammatory disease. New findings from my laboratory provide important new insights into the mechanisms of E-cadherin regulation in epithelia as well as novel approaches to manipulate cadherin activity experimentally. We discovered a mechanism that controls cadherin conformation and adhesive activity at the cell surface independent of any changes in levels of expression or amounts of associated catenins. This included the discovery of E-cadherin activating monoclonal antibodies (mAbs) and a role for p120-catenin phosphorylation and microtubules in the control of E-cadherin activity state. I hypothesize that regulation of the adhesive homophilic bond itself is a key event in cell junction regulation, allowing the catenin-associated cytoskeleton to pull the junctions apart once the adhesive bond is broken, and that this mechanism plays a role in barrier regulation in both epithelia and endothelia during inflammatory processes. The overall goals of this proposal are to determine the roles of cadherin cell surface regulation in the contro of epithelial barrier function and to understand in greater depth the mechanisms by which cadherins are regulated at the cell surface. The specific aims are: A. Investigate the role of E-cadherin activity state in the regulation of the epithelial barrier during inflammatory processes i cell culture and animal models. Regulation by soluble inflammatory mediators, control of neutrophil transmigration, and regulation of the interactions of dendritic cells with epithelium wil be investigated. The role of E-cadherin regulation in vivo will be assessed in an animal model of lung inflammation. B. Determine the mechanisms regulating cadherin adhesive binding activity at the cell surface. Analysis of the structure of epitopes recognized by activity associated mAbs, the biophysical changes in the properties of the homophilic adhesive bond, and the role of cadherin oligomerization, clustering, and localization in adhesion sites, all will provide insights into how the extracellular adhesive domain is regulated. C. Investigate cytoplasmic mechanisms of E-cadherin activation and cell surface regulation. Determining the enzymes that control p120-catenin phosphorylation, the role of microtubules in controlling E-cadherin activity and p120-catenin phosphorylation, and the effectors through which p120-catenin phosphorylation controls adhesion activity, will provide insights into the molecular mechanisms underlying adhesion regulation. Findings from these studies may allow us to develop cadherin- based approaches, or even therapeutics, to manipulate barrier function during inflammation and related disease processes.